A study of the chromospherically active binaries UX Fornacis and AG Doradus

A. Washuettl, K. G. Strassmeier

A&A 370, 218 (2001)


This paper presents a time-series spectrum analysis of the two chromospherically active binary stars UX Fornacis and AG Doradus. To investigate the rotational behaviour in combination with activity in the H$\alpha $ line we obtained almost 40 high-resolution, high-S/N spectra for each system. Both binaries, UX For and AG Dor, show H$\alpha $ of the primary star in absorption but filled in by chromospheric emission while the H$\alpha $ line of the secondaries appear in pure emission. Line variations were seen and are approximately 5-$\sigma$ detections but are not linked to the orbital nor the rotational periods and seem to be erratic. We obtained new orbital elements for both systems and use them in combination with the Hipparcos parallax and our H$\alpha $-spectrum synthesis to determine absolute parameters. We present the first Doppler image of the AG Dor primary using line-profile variations of the FeI $\lambda$6546 line. The image reveals a cool polar feature and three equatorial spots with an average surface temperature difference, photosphere minus spots, of up to 1500 K for the polar spot and $\approx$800 K for the equatorial spots. Since AG Dor is one of the slowest rotators ($v\sin i$=18 kms$^{-1}$) that has ever been Doppler imaged, we present several tests to demonstrate the external consistency of our map.


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August 16, 2000 -- update: May 28, 2001